A type of door that has become increasingly popular, particularly for closets and the like, is a so-called bi-fold door. In a typical opening, four door panels are used. Two of these panels are hinged together at each side of the opening. In a smaller opening, only two door panels are used. The panel nearer the jamb, known as the pivot door, may be pivoted at the top and bottom to support the full weight of both doors. The other panel further from the side of the opening, known as the lead door, typically has guides at the top which run in tracks to keep the edge of the door within the frame.
Thus, when the doors are closed, both doors are in the plane of the frame. To open a pair of doors one pulls at the hinge line, causing the doors to "fold" relative to each other. As the doors open, the pivot door pivots adjacent the jamb and the hinged edge of the lead door swings outwardly as constrained by the hinges between the doors and the guides in the tracks.
The guide tracks used with bi-fold doors are typically elongated U-shaped channels having an elongated projection or ledge extending inwardly from each side of the track. A pivot bracket is seated on or against the pair of ledges and is securely fastened to the track with a screw or similar fastener. Typically, the pivot bracket, which can be relocated in the track, comprises two or more parts which straddle the inwardly directed ledges from above and below and which are held together by the fastener. The pivot bracket provides means for holding a pivot in the pivot door in position within the track.
The pivot bracket commonly provides another function. It has some length along the inside of the track so that when the doors are fully open, there is some "lead" left between the doors. That is, the edges of the fully open doors are spaced apart somewhat in the track by reason of the guide on the lead door striking the end of the pivot bracket. Lead is provided between the doors so that one can close the doors by merely pushing at the hinge line. The lead provides a small angle which lets the lead door commence to move, whereas if edges of the doors were in contact, the doors would be perpendicular to the frame and wouldn't move merely by pushing toward the frame at the hinge line.
When bi-fold doors are slammed open, as commonly happens in service, lateral forces act on the guide tracks and can result in track deformation. The lateral force occurs as the moving doors are stopped. There is an inertial effect tending to make them keep moving. This inertial effect creates a moment causing a lateral force on the track at the location where the lead door guide encounters the end of the pivot bracket. If there is sufficient deformation the pivot bracket can be disengaged from the supporting ledges and popped out of the track, resulting in door failure.
This problem has heretofore been addressed by using stronger tracks, i.e., by making the sides of the tracks thicker, and/or by making the tracks out of stronger materials. Both approaches increase the cost of the tracks.
Accordingly, a need exists for a bi-fold door track assembly that reduces track vulnerability to deformation, yet is inexpensive to manufacture. Such an assembly should be easy to use and install and should be compatible with a variety of bi-fold door designs.